1. Field of the Invention
The present invention relates to a method for manufacturing a hafnium-containing silazane polymer which makes a good ceramic precursor, and a method for manufacturing a ceramic from the polymer.
2. Description of the Prior Art
Although ceramics have attracted attention because of their excellent thermal resistance, abrasion resistance, and high temperature strength, they are difficult to machine because of their hardness and brittleness. For this reason, the steps of manufacturing a ceramic article comprise: preparing a finely ground ceramic powder, compacting the powder into a desired shape, and baking it, e.g., the powder sintering method; or melting an organic polymer ceramic precursor or dissolving the precursor in a solvent, working the viscous liquid into a desired shape, and baking it to render it inorganic, i.e., the precursor method.
The main characteristic of the precursor method is that, it can provide a ceramic article having a configuration which cannot be produced by the powder sintering method. Therefore, the precursor method is virtually the only method that can produce fibrous ceramic articles. Among the materials generally referred to as "ceramics", SiC and Si.sub.3 N.sub.4 are particularly attracting attention because reason of their superior high temperature characteristics. Thus, SiC possesses excellent heat resistance and high temperature strength, and Si.sub.3 N.sub.4 exhibits excellent thermal shock resistance and fracture toughness. Consequently, research into various precursors for these ceramics materials has intensified.
The ceramics obtained through the conventionally known ceramic precursor method are mainly those based on a Si-C-O composition, a Si-O-N composition, and a Si-C-N-O composition. On the other hand, Japanese Patent Kokai No. 56-74126 discloses that a ceramic precursor based on polytitanocarbo silane containing metals, such as, Ti and Zr, can be manufactured by reacting titanoalkoxide with a polycarbo silane.
However, the ceramic obtained by baking the polytitanocarbo silane is based on a Si-Ti-O-C composition and, as such, it contains a considerable amount of oxygen. Also, such a ceramic has a tendency to quickly lose strength at temperatures above 1300.degree. C. because it crystallizes at such temperatures. U.S. Pat. No. 4,312,970 discloses the methods for producing ceramics based on Si-C-N and Si-C-N-O compositions, respectively. However, we have found that these ceramics also undergo crystallization at temperatures above 1300.degree. C., and thus promptly lose their strength.
Also, the ceramics obtained by the conventional ceramic precursor methods tend to have problems in workability and processability, and are low in ceramic yield.
In addition, ceramics based on SiC-Si.sub.3 N.sub.4 composition, which retain the excellent properties inherent to SiC and Si.sub.3 N.sub.4, such as high workability, are also known and disclosed in Japanese Patent Kokai No. 63-193930 and Japanese Patent Kokai No. 63-210133, which teach ceramic manufacturing methods which give an organic silazane polymer and a ceramic made therefrom.